Abstract
Purpose
There have been a number of described techniques for sizing the diameter of radial head implants. All of these techniques, however, are dependent on measurements of the excised native radial head. When accurate sizing is not possible due to extensive comminution or due to a previous radial head excision, it has been postulated that the proximal radioulnar joint (PRUJ) may be used as an intraoperative landmark for correct sizing. The purpose of this study was to: 1) determine if the PRUJ could be used as a reliable landmark for radial head implant diameter sizing when the native radial head in unavailable, and (2) determine the reliability of measurements of the excised radial head.
Method
Twenty-seven fresh-frozen denuded ulnae and their corresponding radial heads (18 males, 9 females) were examined. The maximum diameter (MaxD), minimum diameter (MinD) and dish diameter (DD) of the radial heads were measured twice, 3–5 weeks apart, using digital calipers. Two fellowship-trained upper extremity surgeons, an upper extremity fellow and a senior orthopedic resident were then asked to independently select a radial head implant diameter based on the congruency of the radius of curvature of the PRUJ to that of the radial head trial implants. The examiners were blinded to the native radial head dimensions. This selection was repeated 3–5 weeks later by two of the investigators. Correlation between radial head measurements and radial head implant diameter sizes was assessed using Pearsons correlation coefficient (PCC) and inter and intra-observer reliability were assessed using intra-class correlation coefficient (ICC).
Results
There was a positive correlation between each of the radial head measurements (MaxD, MinD and DD) and the selected radial head implant diameters (PCC of 0.56, 0.59 and 0.51 respectively; p<0.01). Measuring the MaxD, MinD and DD of the radial head showed excellent inter-observer reliability (ICC of 0.99, 1.00 and 0.82 respectively) and excellent intra-observer reliability (ICC of 0.99, 0.98 and 0.75 respectively). The PRUJ sizing method used to determine the diameter of the radial head implant showed poor inter-observer reliability with an ICC of 0.34 but good intra-observer reliability (ICC = 0.76).
Conclusion
Measurements of the diameter of the excised radial head showed excellent intra and inter-observer reliability suggesting that the excised radial head, when available, should be used to select the radial head implant diameter. The inter-observer reliability of using the PRUJ for sizing the diameter of radial head implants was poor, indicating that this method is an unreliable technique for radial head implant diameter sizing. However, the high intra-observer reliability of the PRUJ method indicates that an observer tends to make the same size estimation, even weeks apart. This study suggests that the PRUJ radius of curvature may be different than that of the radial head. Further studies are needed to verify this hypothesis.
